Desert Invader
Sahara Mustard (Brassica tournefortii)
Sahara Mustard is an invasive weed that grows quickly, overtaking native habitats and smothering native plants.
Sahara mustard is the common name for Brassica tournefortii. Other common names are Asian mustard, African mustard, and wild turnip-rape.
Plant Biology
This annual forb germinates in late fall and early winter after seasonal rains.
Its leaves vary in length and are deeply lobed with 8 to 14 toothy lobes per leaf.
Though short-lived, this is a fast growing plant that can reach heights up to 40 inches within just two to three months.
Within 20 to 30 days after germination the plant produces small, dull yellow flowers with tiny petals.
These self-pollinating flowers turn into fruit.
A narrow seed pod, the fruit break open when mature, dropping seeds around the parent plant. A single plant can produce between 750 and 9,000 seeds.
Many seeds also disperse when dried plants break off and tumble across the landscape, scattering seeds along the way.
Photo by Tom Chester
When wet, Sahara mustard seeds form a gel-like (mucilaginous) coating. This allows them to spread by adhering to things like animals, tires, and shoes. It also protects the seeds in water, giving them another avenue of dispersal through waterways.
Protected by the coating or intact within their pods, the ability of Sahara mustard seeds to float across large bodies of water expands their range and threatens shoreline habitats.
As the seeds disperse, they may lie dormant until ideal conditions are met for germination. Seeds have been found to remain viable in the seedbank for 3 or more years.
Environmental Factors
Sahara mustard plants thrive in arid and semi-arid environments.
Sahara mustard is a native plant to north Africa, the Middle East, and Mediterranean areas of southern Europe where it is cultivated for traditional uses.
Humans have unwittingly aided in the spread of Sahara mustard as seeds find their way into ship cargos, tire treads, shoes, and more. No longer confined to its native range, it can be found across continents.
In North America, Sahara mustard has been reported throughout the southwest, rapidly expanding and overtaking desert landscapes as it out-competes native plants.
Sahara mustard thrives in sandy and silty soils . . .
and can be found in rocky, desert scrub soils as well.
An aggressively invasive weed, Sahara mustard is commonly found growing in disturbed sites such as abandoned fields, beaches, and roadsides. Roadsides provide an ideal environment with surface runoff collecting along shoulders. Seeds that have adhered to vehicles, been churned up by grading, or dispersed from the surrounding landscape collect in roadside ditches and establish themselves.
Impacts and Management
Sahara mustard's rapid growth from gemination to senescence is cause for concern in areas where it has invaded, such as the American Southwest. It dominates nutrients and space to crowd out native plants and destroy habitats.
Desert ecosystems are natively fire intolerant with few woody plants and vegetation capable of spreading fires. As invasive plants dry up the dense communities become a wildfire threat. A wildfire fueled by non-native vegetation often burns hotter and faster, permanently altering desert ecosystems.
Photo by William Terry Hunefeld
Control
Early detection and control is the ideal approach to managing weed invasions since well established communities of Sahara mustard can be difficult to eradicate.
Although labor intensive, hand pulling offers the best solution for new invasions where a seed bank has not yet been established. For best control weeds must be pulled before seeds develop and all plant material must be completely removed from the environment. Undeveloped seeds left behind in broken plant material may still continue to develop.
Herbicides can also be used for control but are most effective when applied in the early stages of development, prior to flowering and seed development. Because Sahara mustard germinates earlier and quicker than native species, early herbicide treatment has less of an impact on the development of native species.
Geospatial modeling and analysis can be another valuable tool for managing invasive weeds. Weed locations can be mapped to plan weed control work. And, by incorporating data such as soil types, watershed flow, and road networks, geospatial analysis can be performed to predict where invasions are likely to occur.
Photo by J Prado. Creative Commons license.
Continuous monitoring of current and potentially new Sahara mustard invasions is an important aspect of management. Sahara mustard seeds have been known to survive in the soil for 3 or more years. Repeated visits to monitor treated sites for reoccurrence is critical for curtailing continued infestations.
The ideal plan for controlling a Sahara mustard invasion involves manual control combined with targeted chemical control and continuous monitoring.
Eradicating Sahara mustard from areas it has invaded may be ambitious but it is a worthwhile effort.
Native desert habitats are not just dry, desolate, and uninhabitable regions. They are diverse landscapes filled with a plethora of native plants and wildlife, many of which can only be found in these unique desert environments. And they are all worth saving.
